The present invention relates to novel polyester pellets and a process for preparing the polyester pellets. More particularly, the invention relates to polyester pellets having excellent gas barrier properties, transparency and heat resistance and to a process for preparing the polyester pellets.
Because of their excellent gas barrier properties, transparency and mechanical strength, saturated polyesters such as polyethylene terephthalate are widely used for containers such as bottles. Particularly, the bottles obtained by biaxial stretching blow molding (draw blow molding) of polyethylene terephthalate are excellent in transparency, mechanical strength, heat resistance and gas barrier properties, so that they have been extensively used as containers (PET bottles) to be filled with drinks such as juice, soft drinks and carbonated beverages.
Such bottles are generally produced by a process comprising molding a saturated polyester into a preform having a neck part and a body part, inserting the preform in a mold of given shape, and subjecting the preform to stretching blow molding to stretch the body part, thereby producing a bottle having a neck part and an oriented body part.
The polyester bottles, particularly polyester bottles for drinks such as juice, are required to have heat resistance high enough for heat sterilization of the contents therein, and therefore the bottles are generally further subjected to heat treatment (heat setting) after the blow molding to improve the heat resistance.
In the polyester bottles obtained by the above process, the neck parts are unstretched and inferior to the stretched body parts in the mechanical strength and the heat resistance. In general, therefore, the neck parts of the preforms are heated to crystallize prior to the blow molding, or the necks of the bottles obtained by blow molding are heated to crystallize, thereby improving the neck parts in the mechanical strength and the heat resistance.
In recent years, the sizes of bottles produced from the polyester resins (particularly polyethylene terephthalate) tend to be made smaller. In case of such small-sized bottles, the contact area between the contents and the bottle body part per unit volume is increased, and thus loss of gas or permeation of oxygen from the outside may have a marked influence on the contents, resulting in decrease of shelf life of the contents. Accordingly, the polyester resins are required to have more excellent gas barrier properties than before.
In order to improve the heat resistance and the gas barrier properties of the polyester resins, an attempt to blend polyethylene terephthalate with polyethylene isophthalate has been proposed (see Japanese Patent Publication No. 22302/1989). The blend of polyethylene terephthalate and polyethylene isophthalate, however, generates acetaldehyde when it is melt kneaded at a high temperature to improve compatibility, and this causes problems such as change of taste of the contents filled in the container and lowering of transparency. Further, the polyethylene isophthalate adheres to the screw to prolong the residence time, and this causes another problem of scorching. Furthermore, when polyethylene isophthalate is amorphous, polyethylene terephthalate is required to be dried by an ordinary drier, then cooled and blended in a dry state with the polyethylene isophthalate, followed by molding the blend. Therefore, the cost of equipment for various steps from drying to molding is great, and much space is necessary for the equipment.
To cope with the above problems, there has been proposed a polyester comprising ethylene glycol and a dicarboxylic acid component which comprises terephthalic acid as a major ingredient and isophthalic acid. This polyester, however, does not always have sufficient heat resistance and gas barrier properties and sometimes generates acetaldehyde. Accordingly, development of polyesters having further improved heat resistance and gas barrier properties and hardly generating acetaldehyde is desired.
The present invention has been made with a view to solying such problems in the prior art as mentioned above, and it is an object of the invention to provide crystallized polyester pellets having excellent gas barrier properties, transparency and heat resistance and hardly generating acetaldehyde and to provide a process for preparing the polyester pellets.
The novel polyester pellets according to the invention are polyester pellets made of a polyester which comprises dicarboxylic acid constituent units derived from dicarboxylic acids containing terephthalic acid and isophthalic acid and diol constituent units derived from diols containing ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene, and which has the following properties:
constituent units derived from terephthalic acid are 15 to 99.5% by mol and constituent units derived from isophthalic acid are 0.5 to 85% by mol, both based on the total amount of the dicarboxylic acid constituent units (i),
constituent units derived from ethylene glycol are 25 to 99.5% by mol and constituent units derived from 1,3-bis(2-hydroxyethoxy)benzene are 0.5 to 75% by mol, both based on the total amount of the diol constituent units (ii),
the intrinsic viscosity is in the range of 0.5 to 1.5 dl/g, and
the melting point (Tm (xc2x0 C.)), as measured by a differential scanning calorimeter, satisfies the following formula (I):
[1/527xe2x88x920.0017xc2x7ln(1xe2x88x92(mI+mB)/200)]xe2x88x921xe2x88x92273 less than Tmxe2x89xa6265xe2x80x83xe2x80x83(I) 
wherein mI is a proportion (% by mol) of the constituent units derived from isophthalic acid to all of the dicarboxylic acid constituent units, and mB is a proportion (% by mol) of the constituent units derived from 1,3-bis(2-hydroxyethoxy)benzene to all of the diol constituent units;
said polyester pellets having a density of not less than 1,350 kg/m3.
The melting point (Tm (xc2x0 C.) of the polyester desirably satisfies the following formula (Ixe2x80x2):
[1/527xe2x88x920.0017xc2x7ln(1xe2x88x92(mI+mB)/200)]xe2x88x921xe2x88x92273 less than Tmxe2x89xa6265xe2x80x83xe2x80x83(Ixe2x80x2). 
The acetaldehyde content in the polyester pellets is preferably not more than 20 ppm, particularly preferably not more than 10 ppm.
The process for preparing polyester pellets according to the invention comprises
blending (A) polyethylene terephthalate before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.8 dl/g, in an amount of 99 to 20% by weight, with (B) a polyethylene isophthalate copolymer before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.9 dl/g, in an amount of 1 to 80% by weight, said polyethylene isophthalate copolymer comprising dicarboxylic acid constituent units derived from dicarboxylic acids containing terephthalic acid and isophthalic acid and diol constituent units derived from diols containing ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene,
pelletizing the blend, and
crystallizing the pellets.
It is preferable that the blend is heated to precrystallize it and then subjected to solid phase polymerization.
The blend preferably has a heat-up crystallizing temperature of not higher than 190xc2x0 C.
Another process for preparing polyester pellets according to the invention comprises
blending (C) polyethylene terephthalate after solid phase polymerization having an intrinsic viscosity of 0.5 to 1.5 dl/g, in an amount of 99 to 20% by weight, with (B) a polyethylene isophthalate copolymer before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.9 dl/g, in an amount of 1 to 80% by weight, said polyethylene isophthalate copolymer comprising dicarboxylic acid constituent units derived from dicarboxylic acids containing terephthalic acid and isophthalic acid and diol constituent units derived from diols containing ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene,
pelletizing the blend, and
crystallizing the pellets.
In the present invention, the blend may be subjected to solid phase polymerization after the crystallization.
In any of the above-described processes for preparing polyester pellets according to the invention, the polyethylene isophthalate copolymer (B) preferably has the following properties:
constituent units derived from isophthalic acid to all of the dicarboxylic acid are 50 to 98% by mol and constituent units derived from terephthalic acid are 2 to 50% by mol, both based on the total amount of dicarboxylic acid constituent units (i), and
constituent units derived from ethylene glycol are 15 to 99% by mol and constituent units derived from 1,3-bis(2-hydroxyethoxy)benzene are 1 to 85% by mol, both based on the total amount of diol constituent units (ii).
The polyester pellets according to the invention and the process for preparing the polyester pellets are described in detail hereinafter.
The polyester pellets of the invention are made of a polyester which comprises dicarboxylic acid constituent units derived from dicarboxylic acids containing terephthalic acid and isophthalic acid and diol constituent units derived from diols containing ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene.
It is desirable that the dicarboxylic acid constituent units comprise constituent units derived from terephthalic acid in amounts of 15 to 99.5% by mol, preferably 50 to 99% by mol, and constituent units derived from isophthalic acid in amounts of 0.5 to 85% by mol, preferably 1 to 50% by mol, both based on the total amount of dicarboxylic acid constituent units.
The polyester may contain constituent units derived from dicarboxylic acids other than the isophthalic acid and the terephthalic acid in amounts of less than 20% by mol, within limits not prejudicial to the object of the invention.
Examples of other dicarboxylic acids which may be contained in amounts of less than 20% by mol include:
aromatic dicarboxylic acids, such as phthalic acid (orthophthalic acid), 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, diphenyldicarboxylic acid and diphenoxyethanedicarboxylic acid;
aliphatic dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid and decanedicarboxylic acid; and
alicyclic dicarboxylic acids, such as cyclohexanedicarboxylic acid.
Also employable are ester derivatives of these dicarboxylic acids, and these dicarboxylic acids or their ester derivatives can be used in combination of two or more kinds.
It is desirable that the diol constituent units comprise constituent units derived from ethylene glycol in amounts of 25 to 99.5% by mol, preferably 35 to 99.5% by mol, more preferably 50 to 99.5% by mol, and constituent units derived from 1,3-bis(2-hydroxyethoxy)benzene in amounts of 0.5 to 75% by mol, preferably 0.5 to 65% by mol, more preferably 0.5 to 50% by mol, both based on the total amount of diol constituent units.
The polyester may contain constituent units derived from diols other than the ethylene glycol and the 1,3-bis(2-hydroxyethoxy)benzene in amounts of less than 15% by mol, within limits not prejudicial to the object of the invention.
Examples of other diols which may be contained in amounts of less than 15% by mol include:
aliphatic glycols, such as diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylene glycol, propylene glycol, butanediol, pentanediol, neopentyl glycol, hexamethylene glycol and dodecamethylene glycol;
alicyclic glycols, such as cyclohexanedimethanol;
glycols containing aromatic groups, such as 1,2-bis(2-hydroxyethoxy)benzene and 1,4-(2-hydroxyethoxy)benzene; and
aromatic diols, such as bisphenols, hydroquinone and 2,2-bis(4-xcex2-hydroxyethoxyphenyl)propane.
Also employable are ester derivatives of these diols, and these diols or their ester derivatives can be used in combination of two or more kinds.
Of these diols, preferable is diethylene glycol.
The polyester may further contain units derived from polyfunctional carboxylic acids having 3 or more carboxyl groups and polyhydric alcohols having 3 or more hydroxyl groups within limits not prejudicial to the object of the invention. Specifically, the units derived from the polyfunctional carboxylic acids and/or the units derived from the polyhydric alcohols may be contained in amounts of 0.01 to 5% by mol, preferably 0.05 to 3% by mol, more preferably 0.1 to 1.5% by mol, independently, based on 100% by mol of the dicarboxylic acid units.
It is desirable that the polyester for forming the pellets of the invention has an intrinsic viscosity (TI), as measured in o-chlorophenol at 25xc2x0 C., of 0.50 to 1.5 dl/g, preferably 0.60 to 1.5 dl/g, more preferably 0.7 to 0.9 dl/g.
The melting point (Tm (xc2x0 C.)) of the polyester, as measured by a differential scanning calorimeter, satisfies the following formula (I):
[1/527xe2x88x920.0017xc2x7ln(1xe2x88x92(mI+mB)/200)]xe2x88x921xe2x88x92273 less than Tmxe2x89xa6265xe2x80x83xe2x80x83(I) 
wherein mI is a proportion (% by mol) of the constituent units derived from isophthalic acid to all of the dicarboxylic acid constituent units, and mB is a proportion (% by mol) of the constituent units derived from 1,3-bis(2-hydroxyethoxy)benzene to all of the diol constituent units.
It is preferable that the melting point (Tm (xc2x0 C.)) satisfies the following formula (Ixe2x80x2):
[1/527xe2x88x920.0017xc2x7ln(1xe2x88x92(mI+mB)/200)]xe2x88x921xe2x88x92273 less than Tmxe2x89xa6265xe2x80x83xe2x80x83(Ixe2x80x2). 
In the formulas (I) and (Ixe2x80x2), Tm is preferably not higher than 257xc2x0 C., more preferably not higher than 254xc2x0 C.
The polyester pellets made of such a polyester have a density of not less than 1,350 kg/M3, preferably not less than 1,355 kg/m3, more preferably not less than 1,360 kg/m3, still more preferably not less than 1,380 kg/m3.
The polyester desirably has a heat-up crystallizing calorific value of usually not less than 5 J/g, preferably 7 to 40 J/g.
The polyester pellets of the invention desirably have an acetaldehyde content of not more than 20 ppm, particularly not more than 10 ppm.
There is no specific limitation on the size and the shape of the polyester pellets of the invention, and they are determined appropriately to the use application of the pellets. Examples of the pellet shapes include column-like, elliptic cylindrical, spherical and elliptic spherical shapes. Although the pellet size is not specifically limited, the average diameter of the pellets is usually in the range of about 2.0 to 5.0 mm.
The polyester pellets of the invention can be prepared by the later-described process (1) or (2).
The polyester pellets may optionally contain additives commonly added to polyesters, such as colorants, antioxidants, oxygen absorbents, ultraviolet light absorbers, antistatic agents and flame retardants. In the polyester pellets, recycled PET may be arbitrarily blended. The polyester pellets may furthermore contain resins other than polyesters, such as polyethylene, ionomers, polypropylene and polyester elastomers, if desired.
The polyester pellets of the invention can be used as a material of various molded products such as preforms, bottles, (oriented) films and sheets. These molded products may be laminated ones having at least one layer formed from the polyester pellets of the invention or having at least one layer formed from a blend of the polyester pellets of the invention and another resin. This layer may be any of inner, outer and intermediate layers. Examples of resins for forming other layers include polyesters, such as polyethylene terephthalate and polyethylene isophthalate; polyamides, such as nylon 6; and ethylene/vinyl acetate copolymers. Of these, polyethylene terephthalate is particularly preferable.
Bottles produced from the polyester pellets are excellent in gas barrier properties, transparency and heat resistance. Moreover, the bottles hardly generate acetaldehyde, so that the taste of the contents such as juice does not deteriorate.
Next, the process for preparing polyester pellets according to the invention is described.
The process for preparing polyester pellets according to the invention comprises
blending (A) polyethylene terephthalate before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.8 dl/g, in an amount of 99 to 20% by weight, with (B) a polyethylene isophthalate copolymer before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.9 dl/g, in an amount of 1 to 80% by weight,
pelletizing the blend,
crystallizing the pellets,
and preferably
further subjecting the pellets to solid phase polymerization.
The polyethylene terephthalate (A) for use in the invention comprises dicarboxylic acid units derived from terephthalic acid or its ester derivative and diol units derived from ethylene glycol or its ester derivative.
The dicarboxylic acid units in the polyethylene terephthalate (A) contain terephthalic acid units in amounts of not less than 80% by mol, preferably 85 to 100% by mol, based on 100% by mol of the dicarboxylic acid units.
Examples of other dicarboxylic acids which may be contained in amounts of not more than 20% by mol include:
aromatic dicarboxylic acids, such as phthalic acid (orthophthalic acid), isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, diphenyldicarboxylic acid and diphenoxyethanedicarboxylic acid;
aliphatic dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid and decanedicarboxylic acid; and
alicyclic dicarboxylic acids, such as cyclohexanedicarboxylic acid.
Also employable are ester derivatives of these dicarboxylic acids, and these dicarboxylic acids or their ester derivatives can be used in combination of two or more kinds.
Of these dicarboxylic acids, isophthalic acid is preferable.
The diol units of the polyethylene terephthalate (A) desirably contain ethylene glycol units in amounts of not less than 80% by mol. preferably 85 to 100% by mol, based on 100% by mol of the diol units.
Examples of other diols which may be contained in amounts of not more than 20% by mol include:
aliphatic glycols, such as diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylene glycol, propylene glycol, butanediol, pentanediol, neopentyl glycol, hexamethylene glycol and dodecamethylene glycol;
alicyclic glycols, such as cyclohexanedimethanol;
glycols containing aromatic groups, such as 1,2-bis(2-hydroxyethoxy)benzene, 1,3-bis(2-hydroxyethoxy)benzene and 1,4-(2-hydroxyethoxy)benzene; and
aromatic diols, such as bisphenols, hydroquinone and 2,2-bis(4-xcex2-hydroxyethoxyphenyl)propane.
Also employable are ester derivatives of these diols, and these diols or their ester derivatives can be used in combination of two or more kinds.
Of these diols, preferable are diethylene glycol and cyclohexanedimethanol.
The polyethylene terephthalate for use in the invention may further contain units derived from polyfunctional carboxylic acids having 3 or more carboxyl groups and polyhydric alcohols having 3 or more hydroxyl groups, within limits not prejudicial to the object of the invention. Examples of polyfunctional carboxylic acids are trimesic acid and pyromellitic anhydride, and examples of polyhydric alcohols are glycerol, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, 1,1,1-trimethylolmethane and pentaerythritol.
The polyethylene terephthalate (A) for use in the invention is substantially linear, and this can be confirmed by the fact that the polyethylene terephthalate (A) is dissolyed in o-chlorophenol.
The polyethylene terephthalate (A) desirably has an intrinsic viscosity (xcex7), as measured in o-chlorophenol at 25xc2x0 C., of 0.3 to 0.8 dl/g, preferably 0.35 to 0.75 dl/g, and is a product obtained after liquid phase polymerization and before solid phase polymerization.
It is desirable that the polyethylene terephthalate (A) has a melting point, as measured by a differential scanning calorimeter (DSC, heating rate: 10xc2x0 C./min), of usually 210 to 265xc2x0 C., preferably 220 to 260xc2x0 C., and has a glass transition temperature of usually 50 to 120xc2x0 C., preferably 60 to 100xc2x0 C.
The polyethylene terephthalate (A) may be precrystallized, if necessary. The precrystallization can be carried out by heating the polyethylene terephthalate (A) at a temperature of usually 100 to 220xc2x0 C., preferably 130 to 200xc2x0 C., for about 1 to 360 minutes.
The polyethylene terephthalate (A) can be prepared by a conventional process. For example, the aforesaid dicarboxylic acid and diol are directly esterified and then melt polycondensed in the presence of a polycondensation catalyst such as a germanium compound (e.g. germanium dioxide), an antimony compound (e.g., antimony trioxide, antimony acetate) or a titanium compound (e.g., titanium tetraalkoxide). In another example to prepare the polyethylene terephthalate (A), an ester of the dicarboxylic acid and the diol are subjected to transesterification in the presence of a transesterification catalyst such as a titanium alkoxide (e.g., titanium tetrabutoxide, titanium isopropoxide) or a metallic salt of acetic acid (e.g., cobalt acetate, zinc acetate, magnesium acetate, manganese acetate, calcium acetate). Preferable transesterification catalysts are titanium tetrabutoxide and zinc acetate. Thereafter, the transesteriffication product is subjected to melt polycondensed in the presence of a polycondensation catalyst such as a germanium compound (e.g. germanium dioxide), an antimony compound (e.g., antimony trioxide, antimony acetate) or a titanium compound (e.g., titanium tetraalkoxide). The polycondensation catalyst is desirably used in an amount of 0.0005 to 0.1 part by weight, preferably 0.001 to 0.05 part by weight, based on 100 parts by weight of the total of the dicarboxylic acid (or the dicarboxylic ester) and the diol.
The polyethylene isophthalate copolymer (B) for use in the invention comprises dicarboxylic acid constituent units derived from dicarboxylic acids containing terephthalic acid and isophthalic acid and diol constituent units derived from diols containing ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene.
The dicarboxylic acid constituent units desirably comprise constituent units derived from isophthalic acid in amounts of 50 to 98% by mol, preferably 60 to 95% by mol, and constituent units derived from terephthalic acid in amounts of 2 to 50% by mol, preferably 5 to 40% by mol, based on the total amount of all of the dicarboxylic acid constituent units.
The polyethylene isophthalate copolymer (B) may further contain constituent units derived from dicarboxylic acids other than the isophthalic acid and the terephthalic acid in amounts of less than 15% by mol, within limits not prejudicial to the object of the invention.
Examples of other dicarboxylic acids which may be contained in amounts of less than 15% by mol include:
aromatic dicarboxylic acids, such as phthalic acid (orthophthalic acid), 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, diphenyldicarboxylic acid and diphenoxyethanedicarboxylic acid;
aliphatic dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, sebacic acid, azelaic acid and decanedicarboxylic acid; and
alicyclic dicarboxylic acids, such as cyclohexanedicarboxylic acid.
Also employable are ester derivatives of these dicarboxylic acids, and these dicarboxylic acids or their ester derivatives can be used in combination of two or more kinds.
The diol constituent units desirably comprise constituent units derived from ethylene glycol in amounts of 15 to 99% by mol, preferably 15 to 90% by mol, more preferably 20 to 88% by mol, and constituent units derived from 1,3-bis(2-hydroxyethoxy)benzene in amounts of 1 to 85% by mol, preferably 10 to 85% by mol, more preferably 12 to 80% by mol, based on the total amount of all of the diol constituent units.
The polyethylene isophthalate copolymer (B) may further contain constituent units derived from diols other than the ethylene glycol and the 1,3-bis(2-hydroxyethoxy)benzene in amounts of less than 15% by mol, within limits not prejudicial to the object of the invention.
Examples of other diols which may be contained in amounts of less than 15% by mol include:
aliphatic glycols, such as diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylene glycol, propylene glycol, butanediol, pentanediol, neopentyl glycol, hexamethylene glycol and dodecamethylene glycol;
alicyclic glycols, such as cyclohexanedimethanol;
glycols containing aromatic groups, such as 1,2-bis(2-hydroxyethoxy)benzene and 1,4-(2-hydroxyethoxy)benzene; and
aromatic diols, such as bisphenols, hydroquinone and 2,2-bis(4-xcex2-hydroxyethoxyphenyl)propane.
Also employable are ester derivatives of these diols, and these diols or their ester derivatives can be used in combination of two or more kinds.
Of these diols, preferable is diethylene glycol.
The polyethylene isophthalate copolymer (B) may further contain units derived from such polyfunctional carboxylic acids having 3 or more carboxyl groups and such polyhydric alcohols having 3 or more hydroxyl groups as previously described with respect to the polyethylene terephthalate (A), within limits not prejudicial to the object of the invention. Specifically, the units derived from the polyfunctional carboxylic acids and/or the units derived from the polyhydric alcohols may be contained in amounts of 0.05 to 0.4% by mol, preferably 0.1 to 0.35% by mol, more preferably 0.2 to 0.35% by mol, independently, based on 100% by mol of the dicarboxylic acid units.
The polyethylene isophthalate copolymer (B) desirably has an intrinsic viscosity (xcex7), as measured in o-chlorophenol at 25xc2x0 C., of 0.3 to 0.9 dl/g, preferably 0.35 to 0.85 dl/g, and is a product obtained after liquid phase polymerization and before solid phase polymerization.
The polyethylene isophthalate copolymer (B) desirably has a glass transition temperature, as measured by a differential scanning calorimeter (DSC, heating rate: 10xc2x0 C./min), of usually 40 to 120xc2x0 C., preferably 50 to 100xc2x0 C.
The polyethylene isophthalate copolymer (B) may be precrystallized, if necessary, similarly to the polyethylene terephthalate (A).
The polyethylene isophthalate copolymer (B) can be prepared by a conventional process. For example, the aforesaid dicarboxylic acid and diol are directly esterified and then melt polycondensed in the presence of a polycondensation catalyst such as a germanium compound (e.g. germanium dioxide), an antimony compound (e.g., antimony trioxide, antimony acetate) or a titanium compound (e.g., titanium tetraalkoxide). In another example to prepare the polyethylene isophthalate copolymer (B), an ester of the dicarboxylic acid and the diol are subjected to transesterification in the presence of a transesterification catalyst such as a titanium alkoxide (e.g., titanium tetrabutoxide, titanium isopropoxide) or a metallic salt of acetic acid (e.g., cobalt acetate, zinc acetate, magnesium acetate, manganese acetate, calcium acetate). Preferable transesterification catalysts are titanium tetrabutoxide and zinc acetate. Thereafter, the transesteriffication product is subjected to melt polycondensed in the presence of a polycondensation catalyst such as a germanium compound (e.g. germanium dioxide), an antimony compound (e.g., antimony trioxide, antimony acetate) or a titanium compound (e.g., titanium tetraalkoxide).
In the process of the invention, 99 to 20% by weight, preferably 99 to 40% by weight, more preferably 98 to 50% by weight, of the polyethylene terephthalate (A) and 1 to 80% by weight, preferably 1 to 60% by weight, more preferably 2 to 50% by weight, of the polyethylene isophthalate copolymer (B) are blended with each other.
The blending is carried out by mixing the polyethylene terephthalate (A) with the polyethylene isophthalate copolymer (B) in the above mixing ratio and melt kneading them at 260 to 310xc2x0 C. for 2 to 300 seconds. After the kneading, the resulting blend is processed into chips (pellets) by means of an extruder or the like. The average diameter of the pellets is preferably in the range of 2.0 to 5.0 mm.
In the blending of the polyethylene terephthalate (A) with the polyethylene isophthalate copolymer (B), a transesterification catalyst and a lubricant may be optionally added.
Examples of the transesterification catalysts include germanium dioxide, antimony trioxide, antimony acetate, manganese acetate, magnesium acetate, cobalt acetate, calcium acetate, zinc acetate and titanium tetrabutoxide. The transesterification catalyst is desirably used in an amount of 0.0005 to 0.1 part by weight, preferably 0.001 to 0.05 part by weight, based on 100 parts by weight of the blend.
Examples of the (external) lubricants include magnesium stearate and calcium stearate. The lubricant may be externally added in an amount of 0.0005 to 0.1 part by weight, preferably 0.001 to 0.05 part by weight, based on 100 parts by weight of the blend.
The resulting blend desirably has a heat-up crystallizing temperature (Tcc) of not higher than 190xc2x0 C., preferably not higher than 180xc2x0 C., more preferably 120 to 170xc2x0 C.
The heat-up crystallizing temperature (Tcc) is determined, using a differential scanning calorimeter of DSC-7 model manufactured by Perkin Elmer Co., in the following manner.
A sample of about 10 mg is collected from the center of the chip of the polyester blend which has been dried under a pressure of about 15 mmHg at about 140xc2x0 C. for at least about 5 hours. The sample is introduced in an aluminum pan for liquids of the DSC in a nitrogen atmosphere, and the pan is closed. The sample is first rapidly heated from room temperature at a heating rate of 320xc2x0 C./min, maintained at 290xc2x0 C. for 10 minutes under melting, thereafter rapidly cooled to room temperature at a cooling rate of 320xc2x0 C./min, maintained at room temperature for 10 minutes and finally heated at a heating rate of 10xc2x0 C./min, to detect exothermic peaks, and the temperature at the maximum peak is found.
The blend desirably has an intrinsic viscosity, as measured in o-chlorophenol at 25xc2x0 C., of 0.3 to 0.9 dl/g, preferably 0.35 to 0.85 dl/g.
The pellets of the blend obtained as above are then crystallized.
Crystallization of the pellets is carried out by maintaining the pellets in a dry state at a temperature of not lower than the glass transition temperature (Tg) and lower than the melting point, preferably a temperature higher than Tg by 20xc2x0 C. and lower than the melting point by 40xc2x0 C., for 1 to 300 minutes, preferably 5 to 200 minutes. More specifically, the pellets may be heated at a temperature of 80 to 210xc2x0 C., preferably 100 to 180xc2x0 C.
The crystallization can be carried out in air or in an inert gas atmosphere.
The polyester blend thus crystallized desirably has a crystallinity of 20 to 50%.
In the crystallization, solid phase polymerization of polyester does not proceed, so that the intrinsic viscosity of the polyester blend after the crystallization is almost equal to the intrinsic viscosity of the polyester blend before the crystallization, and the difference between the intrinsic viscosity of the polyester blend before and after the crystallization is usually not more than 0.06 dl/g.
By the crystallization of the polyester blend, the acetaldehyde content in the polyester can be decreased.
In the present invention, the crystallized blend may be subjected to solid phase polymerization, if desired. The crystallization conducted before solid phase polymerization is sometimes referred to as xe2x80x9cprecrystallizationxe2x80x9d.
The solid phase polymerization is carried out at a temperature of usually 180 to 230xc2x0 C., preferably 190 to 220xc2x0 C. In the solid phase polymerization, the pellets of the blend are desired to be in a dry state, and therefore the pellets of the blend may be beforehand dried at a temperature of 80 to 180xc2x0 C.
The polyester pellets obtained after the solid phase polymerization have an intrinsic viscosity (xcex7), as measured in o-chlorophenol at 25xc2x0 C., of 0.5 to 1.5 dl/g, preferably 0.6 to 1.5 dl/g, more preferably 0.6 to 1.2 dl/g. It is desirable that this intrinsic viscosity is about 1.1 to 2.5 times, preferably 1.2 to 2.0 times, greater than the intrinsic viscosity of the blend before the solid phase polymerization.
The polyester pellets may be then subjected to a hot water treatment. The hot water treatment can be carried out by immersing the polyester pellets in hot water of 70 to 120xc2x0 C. for 1 to 360 minutes. Through the hot water treatment, the catalyst used for the polyester polycondensation reaction can be deactivated.
The polyester pellets obtained by the process of the invention may optionally contain additives commonly added to polyesters, such as colorants, antioxidants, oxygen absorbents, ultraviolet light absorbers, antistatic agents and flame retardants.
The polyester pellets prepared by the process of the invention can be used as a material of various molded products such as preforms, bottles, (oriented) films and sheets. The bottles produced from the polyester pellets are excellent in gas barrier properties, transparency and heat resistance. Moreover, the bottles hardly generate acetaldehyde, so that the taste of the contents such as juice does not deteriorate.
Another process for preparing polyester pellets according to the invention comprises the steps of:
blending (C) polyethylene terephthalate after solid phase polymerization having an intrinsic viscosity of 0.5 to 1.5 dl/g, in an amount of 20 to 99% by weight, with (B) a polyethylene isophthalate copolymer before solid phase polymerization having an intrinsic viscosity of 0.3 to 0.9 dl/g, in an amount of 1 to 80% by weight,
pelletizing the blend,
crystallizing the pellets,
and preferably
further subjecting the pellets to solid phase polymerization.
The polyethylene terephthalate (C) for use in the invention comprises dicarboxylic acid units derived from terephthalic acid or its ester derivative and diol units derived from ethylene glycol or its ester derivative.
The dicarboxylic acid units in the polyethylene terephthalate (C) desirably contain terephthalic acid units in amounts of not less than 80% by mol, preferably 85 to 100% by mol, based on 100% by mol of the dicarboxylic acid units.
Examples of other dicarboxylic acids which may be contained in amounts of not more than 20% by mol include those dicarboxylic acids as previously exemplified with respect to the polyethylene terephthalate (A). Particularly preferable is isophthalic acid.
The diol units in the polyethylene terephthalate (C) desirably contain ethylene glycol units in amounts of not less than 80% by mol, preferably 85 to 100% by mol, based on 100% by mol of the diol units.
Examples of other diols which may be contained in amounts of not more than 20% by mol include those diols as previously exemplified with respect to the polyethylene terephthalate (A). Particularly preferable are diethylene glycol and cyclohexanedimethanol.
The polyethylene terephthalate (C) may further contain units derived from polyfunctional carboxylic acids having 3 or more carboxyl groups and polyhydric alcohols having 3 or more hydroxyl groups, within limits not prejudicial to the object of the invention. Examples of polyfunctional carboxylic acids are trimesac acid and pyromellitic anhydride, and examples of polyhydric alcohols are glycerol, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, 1,1,1-trimethylolmethane and pentaerythritol.
The polyethylene terephthalate (C) is substantially linear, and this can be confirmed by the fact that the polyethylene terephthalate (C) is dissolyed in o-chlorophenol.
The polyethylene terephthalate (C) desirably has an intrinsic viscosity (T), as measured in o-chlorophenol at 25xc2x0 C., of 0.5 to 1.5 dl/g, preferably 0.6 to 1.1 dl/g, and in a product obtained after solid phase polymerization.
It is desirable that the polyethylene terephthalate (C) has a melting point, as measured by a differential scanning calorimeter (DSC, heating rate: 10xc2x0 C./min), of usually 230 to 270xc2x0 C., preferably 240 to 260xc2x0 C., and has a glass transition temperature of usually 58 to 75xc2x0 C., preferably 60 to 70xc2x0 C.
The polyethylene terephthalate (C) can be prepared by a conventional process. For example, the aforesaid dicarboxylic acid and diol are directly esterified, then melt polycondensed in the presence of a polycondensation catalyst such as a germanium compound (e.g. germanium dioxide), an antimony compound (e.g., antimony trioxide, antimony acetate) or a titanium compound (e.g., titanium tetraalkoxide) and subjected to solid phase polymerization. In another example to prepare the polyethylene terephthalate (C), an ester of the dicarboxylic acid and the diol are subjected to transesterification in the presence of a transesterification catalyst such as a titanium alkoxide (e.g., titanium tetrabutoxide, titanium isopropoxide) or a metallic salt of acetic acid (e.g., cobalt acetate, zinc acetate, magnesium acetate, manganese acetate, calcium acetate). Preferable transesterification catalysts are titanium tetrabutoxide and zinc acetate. Thereafter, the transesteriffication product is subjected to melt polycondensed in the presence of a polycondensation catalyst such as a germanium compound (e.g. germanium dioxide), an antimony compound (e.g., antimony trioxide, antimony acetate) or a titanium compound (e.g., titanium tetraalkoxide) and subjected to solid phase polymerization. The solid phase polymerization is carried out by heating the melt polycondensation product at a temperature of usually 180 to 230xc2x0 C., preferably 190 to 220xc2x0 C. In the solid phase polymerization, the melt polycondensation product is desired to be in a dry state, and therefore the melt polycondensation product may be beforehand dried at a temperature of 80 to 180xc2x0 C.
The polyethylene isophthalate copolymer (B) comprises dicarboxylic acid constituent units derived from dicarboxylic acids containing terephthalic acid and isophthalic acid and diol constituent units derived from diols containing ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene. This polyethylene isophthalate copolymer (B) is the same as the polyethylene isophthalate copolymer (B) previously described with respect to the process (1) of the present invention.
In the process of the invention, 99 to 20% by weight, preferably 99 to 40% by weight, more preferably 98 to 50% by weight, of the polyethylene terephthalate (C) and 1 to 80% by weight, preferably 1 to 60% by weight, more preferably 2 to 50% by weight, of the polyethylene isophthalate copolymer (B) are blended with each other.
The blending is carried out by mixing the polyethylene terephthalate (C) with the polyethylene isophthalate copolymer (B) in the above mixing ratio and melt kneading them at 260 to 310xc2x0 C. for 30 to 300 seconds. After the kneading, the resulting blend is pelletized by means of an extruder or the like. The average diameter of the pellets is preferably in the range of 2.0 to 5.0 mm.
In the blending of the polyethylene terephthalate (C) with the polyethylene isophthalate copolymer (B), a transesterification catalyst and a lubricant may be added, as described for the process (1) of the invention.
The resulting blend desirably has an intrinsic viscosity, as measured in o-chlorophenol at 25xc2x0 C., of 0.3 to 0.9 dl/g, preferably 0.35 to 0.85 dl/g.
The blend desirably has a heat-up crystallizing temperature (Tcc) of not higher than 170xc2x0 C., preferably not higher than 160xc2x0 C., more preferably 100 to 155xc2x0 C.
The pellets of the blend obtained as above are then crystallized.
Crystallization of the pellets is carried out by maintaining the pellets in a dry state at a temperature of not lower than the glass transition temperature (Tg) and lower than the melting point, preferably a temperature higher than Tg by 20xc2x0 C. and lower than the melting point by 40xc2x0 C., for 1 to 300 minutes, preferably 5 to 200 minutes. More specifically, the pellets may be heated at a temperature of 80 to 210xc2x0 C., preferably 100 to 180xc2x0 C.
The crystallization can be carried out in air or in an inert gas atmosphere.
The polyester blend thus crystallized desirably has a crystallinity of 20 to 50%.
In the crystallization, solid phase polymerization of polyester does not proceed, so that the intrinsic viscosity of the polyester blend after the crystallization is almost equal to the intrinsic viscosity of the polyester blend before the crystallization, and the difference between the intrinsic viscosity of the polyester blend before and after the crystallization is usually not more than 0.06 dl/g.
In the present invention, the pellets may be subjected to solid phase polymerization after the crystallization. The solid phase polymerization is carried out at a temperature of usually 180 to 230xc2x0 C., preferably 190 to 220xc2x0 C., as described for the process (1). In the solid phase polymerization, the pellets of the blend are desired to be in a dry state, and therefore the pellets of the blend may be beforehand dried at a temperature of 80 to 180xc2x0 C.
The polyester pellets may be then subjected to a hot water treatment, as described for the process (1). The hot water treatment can be carried out by immersing the solid phase polymerization product in hot water of 70 to 120xc2x0 C. for 1 to 360 minutes.
The polyester pellets obtained by the process of the invention may optionally contain additives commonly added to polyesters, such as colorants, antioxidants, oxygen absorbents, ultraviolet light absorbers, antistatic agents and flame retardants.
The polyester pellets prepared by the process of the invention can be used as a material of various molded products such as preforms, bottles, (oriented) films and sheets. The bottles produced from the polyester pellets are excellent in gas barrier properties, transparency and heat resistance. Moreover, the bottles hardly generate acetaldehyde, so that the taste of the contents such as juice does not deteriorate.
By the use of the polyester pellets of the invention, a dry feed line of materials to an injection molding machine or an extruder can be extremely simplified, so that the cost of equipment can be sharply reduced. Further, molded products of the polyester pellets can be prominently prevented from scorching even when molding is continuously carried out for a long period of time. Moreover, the molded products are excellent in gas barrier properties, transparency and heat resistance and have a low content of acetaldehyde. Particularly, bottles of the polyester pellets not only have such excellent properties but also exhibit such high strength that delamination hardly takes place even when they are cut with a knife.